Galileo: the man

THE ADVENTURE BEGUN BY GALILEO

Almost 400 years ago, in Padua, Galileo Galileo pointed his telescope towards the Moon, thus using for the first time an instrument to observe the celestial objects, after thousands of years in which the sky was observed with the naked eye. This happened in 1609, and since then the progress of astronomical knowledge has always depended on the development of newer and better instruments of investigation. Nevertheless, in order to be understood, the observations need human interpretation and intuition, just as in the past.

GALILEO GALILEI'S TELESCOPE

This eighteenth century copy reproduces one of the many telescopes built by Galileo, made of two lenses, the objective and the the eyepiece, that are kept in the right distance by a cardboard tube or, as in this case, a wooden one, coated with leather. The magnifying power was 20 times approximately. The great scientist used an instrument such as this one to carry out the observations that convinced him about the validity of the Copernican system.
(Optical collection and glasses - Luxottica)

DIALOGUE CONCERNING THE TWO CHIEF WORLD SYSTEMS

First edition of the 'Dialogo sui massimi sistemi' (Florence, 1632), with notes and corrections made by Galileo Galilei himself. This is the book where Galileo enunciates the principles of the Copernican theory. A few months after its publication, the book was forbidden. (JPEG, 115 K)
(Library of the Bishop's Seminary in Padova)

SIDEREUS NUNCIUS (Venice 1610)

Reproduction of the front-page of the work in which Galileo describes his greatest discoveries. (JPEG, 481 K)
(Florence National Library. Photo: Franco and Matteo Danesin)

DIANOIA ASTRONOMICA (Venice 1611)

Reproduction of the front-page of the work by Francesco Sizzi of Florence, in which he challenged the thesis of Sidereus Nuncius. The impact of Galileo's discoveries produces at the time a great amount of literature, both in his favour and in open contrast. (JPEG, 411 K) (The Babele Library by Giancarlo Beltrame. Photo: Franco and Matteo Danesin)

ASTROLABE OF THE YEAR 1573.

The Astrolabe became known in Europe in the Middle Ages, brought by Arab scientists, and was used especially to determine the position of the Sky and the stars in the sky, and, therefore, the date and the time. This specimen was built in Mantova by Adrien Descrolieres, and marks the position of 22 stars. Galileo used many telescopes such as this for his astronomical calculations.
(Giancarlo Beltrame Collection)

PORTABLE TERRESTRIAL/CELESTIAL TELESCOPE

This portable globe, which can also be opened, was build by the Englishman N. Lane towards the end of the eighteenth century, in wood and paper. The inner surface presents the two celestial hemispheres with the constellation. Similar objects were very fashionable at the time.
(Giancarlo Beltrame Collection)

ZEISS EIGHTEENTH CENTURY TELESCOPE

Lens telescope built by Carl Zeiss of Jena in 1810.
Its opening measures 80 millimetres and its focal length 1,200 millimetres. It has three different eyepieces, and it can reach from 30 to 67 enlargements.

(Zeiss)

Experiments and studies in order to produce better instruments have never stopped, but it is only in our century that the instruments that worked with lenses have been replaced by reflecting telescopes.
Later, with the development of instruments such as the spectroscope, modern astrophysics began. The spectroscope, basically made of a prism, allows to resolve light into the various colours, thus obtaining its spectral components. The study of the spectra allows to understand the nature of the body that emitted the light: its temperature, its chemical composition and even its motion. A new vast field of studies, astrophysics, has been opened by the use of spectroscopes applied to telescopes.

THE ORION CONSTELLATION

Autograph drawings by Galileo of the Orion constellation (Cinguli et ensis Orionis asterismus) (JPEG, 299 K) and the same part of the constellation photographed with a small enlargement, with the homonymous nebula. (JPG, 140 K)
(National Library of Florence. Photo: Franco and Matteo Danesin) (Photo: SAIt)

THE PLEIADES CLUSTER

Drawings by Galileo of the Pleiades cluster in the Taurus constellation, from the Sidereus Nuncius (JPEG, 165 K), and a modern picture of the Pleiades, which are stars still in formation, surrounded by dust and gas (JPEG, 48 K). It can be noted that Galileo could see a lot more stars than one could see today using the same telescope, due to the luminous pollution that gradually prevents us from admiring the starry sky.
(Photo: Franco and Matteo Danesin)

THE CRATERS OF THE MOON
With his very accurate observations of the Moon, Galileo destroyed one of the absolute certainties of the time; it was thought, in fact, that our satellite was a perfect and uniform sphere. The exaggeration of the size of the craters drawn by him had a precise didactic reason, to obtain a better understanding of the light/shadow effect caused by the light of the Sun on the hills and the depressions on the lunar surface. "And on the Earth, before Dawn, while darkness still occupies the plain, aren't the peaks of the highest mountains illuminated by the solar rays?" (JPEG, 307 K)
(National Library of Florence. Photo: Franco and Matteo Danesin)

The Moon photographed by the Galileo probe. (JPEG, 42 K)
(NASA-JPL)

THE PHASES OF VENUS
The planet Venus, during its revolution around the Sun, is illuminated so to form, as does the Moon around the Earth, 'phases'. This seventeenth century drawing explains the mechanism, guessed and verified by Galileo in 1610, and is an irrefutable evidence in favour of the Copernican system. In his own words: "Cynthiae figuras aemulatur mater amorum" ( the mother of Cupid (Venus) imitates the configuration of Cynthia (the Moon)).
(JPEG, 230 K)

The upper layers of the cloud of Venus photographed in violet light by the Galileo probe in 1990.
(JPEG, 24 K) (NASA-JPL)

THREE-BODIED SATURN
Saturn, the majestic gaseous planet which is surrounded by an outstanding ring system, can be seen from the Earth during its revolution motion, under different inclinations. Therefore, its rings can be sometimes seen edge on, and some other times more face one. Galileo could not understand the nature of the rings, due to the limited resolving power of its instrument. In 1610, he described the "very strange marvel" of Saturn, which is "composed of three". It was the Dutch astronomer Huygens, who, in 1659, discovered the rings with a better telescope. (JPEG, 154 K)
(NASA-JPL)

Drawing that explains the different perspective of the rings, as seen from the Earth.
(JPEG, 127 K)

THE SUN SPOTS
According to the Aristotelians the Sun was pure and incorruptible. Galileo demonstrated the the spots belonged to the surface, and, besides, he understood from their motion that the Sun does not rotate on its own axis. According to his instructions: "In order to observe distinct spots one should darken the room by closing all windows, so that no light enters the room except through the telescope, and one should apply to the telescope a wide piece of paper, that casts a shadow over the drawing paper, thus preventing the light of the Sun from falling on it, except for the light that passes through the glasses of the telescope". (JPEG, 25 K)
(Photo SAIt)

THE MILKY WAY

How surprised Galileo was when he saw how many more stars he could see through the telescope! "What we observed... was the essence or the matter of the Milky Way, which can be seen so evidently through the telescope that all discussions, that have been the worry of philosophers for so many centuries, vanish with the certainly of experience... In fact, the Galaxy is nothing but a set of innumerable stars disseminated into clusters; because whichever direction one chooses for the telescope, immediately a very large number of stars can be seen". (JPEG, 675 K)
(Photo: Anglo-Australian Telescope Board)

"On the day of January 7th, 1610 Jupiter could be observed with the telescope, as well as three fixed stars, none of which was visible without the telescope"

THE MEDICEAN CELESTIAL BODIES
Since January 7th, 1610, Galileo began to take notes, night after night, of the position of three at first, then four "small stars" discovered to be close to the planet Jupiter which did not behave like fixed stars, but continuously moved with respect to the planet. He soon reached the conclusion that those were satellites just like our Moon: "experience shows us four stars wandering around Jupiter, as does the Moon around the Earth, while travelling on an orbit around the Sun together with Jupiter, with a period of twelve years". So the doubts of those who at the time were so much troubled by the motion of the Moon around the Earth, vanished. Galileo dedicated his discovery to Cosimo II of Medici by calling the new objects "medicea sidera". (JPEG, 401 K)
(National Museum of Florence. Photo: Franco and Matteo Danesin)

The medicean satellites photographed by Hubble Space Telescope in 1995. (JPEG, 46 K)
(NASA-STScI)

Callisto (JPEG, 340 K) and the volcanos on Io (JPEG, 224 K)

Io, Europa, Ganymede and Callisto, the four main satellites of Jupiter, the medicean objects discovered by Galileo, and now also called "Galilean", have been revealed for the first time by the images of the two Voyager missions in the eighties.
(NASA-JPL)

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